JP2002006226A - Inspecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extremely accurately inspect an object to be inspected having fine shape by making optical frequency response optimum in accordance with the inspection spot of the object to be inspected without depending on only the short wavelength of illuminating light and the high NA of an objective lens. SOLUTION: Inspection is performed while switching the intensity distribution of a DUV laser beam on the surface of the aperture diaphragm 12 of an illumination optical system so as to be optimum distribution in accordance with the pattern shape of the inspection spot on a semiconductor wafer 100 and an inspection purpose.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating an inspection portion of an inspection object with illumination light, and detecting reflected light, scattered light and diffracted light from the inspection portion illuminated by the illumination light.
The present invention relates to an inspection device that inspects a state of an inspection location.

[0002]

2. Description of the Related Art In recent years, with the progress of digitalization in the field of the electric industry, the degree of integration of semiconductor chips has been actively increased. How to efficiently provide such highly integrated semiconductor chips at low cost has become an important issue that will determine the development of the digital electric industry in the future.

In order to efficiently produce semiconductor chips at low cost, it is important to quickly and accurately detect problems that occur during the manufacturing process. For this reason, there is an increasing demand for an inspection apparatus capable of accurately inspecting a fine circuit pattern formed on a semiconductor chip.

In general, an inspection apparatus using an optical microscope is often used as an inspection apparatus for inspecting a fine pattern represented by a circuit pattern of a semiconductor chip. Inspection equipment using an optical microscope irradiates the inspection location of the inspection object with illumination light and optically detects the reflected light, scattered light, diffracted light, refracted light, etc., and inspects the state of the inspection location. I am trying to do it.

[0005] Meanwhile, the circuit pattern of a semiconductor chip tends to be further miniaturized, and in recent years, the line width is 0.18 μm.
m or less design rules are being applied. In order to inspect such a very fine pattern with high accuracy, in the field of an inspection apparatus, a high resolution greatly exceeding the resolution of an existing optical microscope has been required.

As a microscope capable of obtaining high resolution, a scanning electron microscope (SEM: Scanning Electron Microscop) is used.
e) and Atomic Force Microsco (AFM)
pe), Near-field scanning optica
l Microscope) has been developed. Inspection with such a microscope enables high-resolution inspection, but requires that the inspection environment be evacuated and that inspection takes a long time due to the narrow field of view. The inspection principle itself becomes a hindrance factor for increasing the throughput.

In recent years, laser microscopes using laser light having a single wavelength as illumination light have been actively developed. Then, a light source device capable of continuously oscillating short-wavelength deep ultraviolet laser light has been put to practical use. By using this light source device as an illumination light source, it can be satisfied as an inspection device for inspecting a fine circuit pattern in a semiconductor chip. A level of resolution has been obtained.

If an inspection apparatus is constructed using such a laser microscope, a fine pattern can be inspected with high resolution with high accuracy, and a high throughput can be realized and a quick inspection can be performed. As a device for measuring the size of a fine pattern and detecting a fine defect like a circuit pattern of a chip, strong expectation is given.

[0009]

In putting the above-described inspection apparatus into practical use, in order to perform inspection of fine patterns more appropriately, optimal optical characteristics are obtained according to the fine patterns to be inspected. It is hoped that Up to now, the improvement of the optical characteristics of the inspection apparatus has been realized by improving the resolution by shortening the wavelength of the illumination light and increasing the numerical aperture (NA) of the objective lens. However, in order to shorten the wavelength of the illumination light and increase the NA of the objective lens, extremely expensive development costs, material costs, processing costs, and the like are required. It is difficult from the viewpoint of cost to realize only by shortening the wavelength of light and increasing the NA of the objective lens.

Therefore, the present invention is to optimize the optical frequency response in accordance with the inspection location of the inspection object without relying only on shortening the wavelength of the illumination light and increasing the NA of the objective lens.
An object of the present invention is to provide an inspection apparatus capable of inspecting an inspection object having a fine shape with extremely high accuracy.

[0011]

It is known that the optical characteristics of an actual microscope greatly depend on the intensity distribution of illumination light on an aperture stop surface of an illumination system. That is,
In an illumination system that is partially coherent, by changing the diameter of the aperture stop of the illumination system, the optical characteristics such as the resolution limit, contrast, and coherence greatly change. Therefore, if the intensity distribution of the illumination light on the aperture stop surface of the illumination system is optimized according to the fine pattern to be inspected, optimal optical characteristics according to the fine pattern can be obtained.

An inspection apparatus according to the present invention has been devised based on the above knowledge, and includes a support means for supporting an object to be inspected, and an inspection portion of the object to be inspected supported by the support means. Illuminating means for irradiating monochromatic light in a predetermined wavelength range as illuminating light; detecting means for detecting reflected light, scattered light, and diffracted light from an inspection location illuminated by the illuminating light; and output from the detecting means. Inspection means for inspecting the state of the inspection location based on the The inspection apparatus is characterized in that the illumination means has a switching means for switching the intensity distribution of the illumination light in the plane of the aperture stop according to the structure of the inspection location and the purpose of the inspection.

In this inspection apparatus, the object to be inspected is supported by the support means. Then, the illuminating unit irradiates monochromatic light in a predetermined wavelength range as illumination light to the inspection location of the inspection object supported by the supporting unit. At this time, the switching means of the illuminating means switches the intensity distribution of the illuminating light in the aperture stop plane so as to be optimum according to the structure of the inspection location and the inspection purpose. Thereby, the inspection location is irradiated with the optimum illumination light according to the structure of the inspection location and the purpose of the inspection.

The illumination light applied to the inspection location is reflected, scattered, and diffracted according to the state of the inspection location.
The reflected light, scattered light, and diffracted light from these inspection locations are detected by the detecting means. And these reflected light, scattered light,
Based on the output from the detection means corresponding to the diffracted light, the state of the inspection object is inspected by the inspection means.

In this inspection apparatus, as described above, the illumination light optimal for the structure of the inspection location and the purpose of the inspection is applied to the inspection location, and the reflected light, the scattered light, and the diffracted light output from the detecting means. Since the state of the inspection location is inspected based on the output, highly accurate inspection is possible.

In this inspection apparatus, it is desirable that the illuminating means has an ultraviolet laser light source for emitting laser light in an ultraviolet wavelength range. If the laser light in the ultraviolet wavelength range emitted from the ultraviolet laser light source is used as illumination light, the state of the inspection location can be inspected more accurately.

In this inspection apparatus, the illuminating means switches between a first illumination system for illuminating the inspection location with Koehler illumination and a second illumination system for illuminating the inspection location with critical illumination. It is desirable to have a means. If the switching means can switch between a first illumination system that illuminates the inspection location with Koehler illumination and a second illumination system that illuminates the inspection location with critical illumination, for example, inspection of the inspection object can be performed. As in the case where the first illumination system is selected when inspecting a portion, and the second illumination system is selected when adjusting the intensity distribution of the illumination light in the aperture stop plane, according to the purpose. An optimal illumination system can be selected.

Further, in this inspection apparatus, it is desirable that the illumination means has a coherence reducing means for reducing the coherence of the illumination light. If the coherence of the illumination light is reduced by the coherence reducing means,
The uniformity of the illumination light can be improved.

In this inspection apparatus, the illuminating means includes a light amount monitoring means for monitoring the amount of the illuminating light, and a shutter for switching transmission or blocking of the illuminating light according to the amount of the illuminating light detected by the light amount monitoring means. It is desirable to have means. In this way, if the amount of illumination light is monitored by the monitoring means, and the shutter means switches the transmission or blocking of the illumination light accordingly, the irradiation light quantity of the illumination light can be adjusted according to the inspection location. Because it can do, without damaging the inspection location,
The inspection of the inspection location can be appropriately performed.

In this inspection apparatus, there is provided a focus control means for controlling the focus state between the detection means and the inspection position of the inspection object supported by the support means based on the output from the distance sensor. The control unit switches the illumination unit to the second illumination system and detects a focus error amount caused by the accuracy of the support surface of the support unit based on information obtained by illuminating the inspection location with the critical illumination. It is desirable to correct the output from the distance sensor according to the focus error amount and perform focus control. As described above, the focus unit detects the focus error amount due to the accuracy of the support surface of the support unit based on the information obtained by illuminating the inspection location with the critical illumination, and detects the distance sensor according to the focus error amount. If the focus control is performed by correcting the output from the camera, the focus control can be realized with extremely high accuracy, and the state of the inspection location can be inspected with higher accuracy.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. Here, an example in which the present invention is applied to an inspection apparatus that inspects a circuit pattern in a semiconductor chip will be described. However, the present invention is not limited to the examples described here, and an inspection of an inspection target having a fine shape is performed. It can be widely applied to inspection devices to be performed.

A semiconductor chip is manufactured by forming a large number of circuit patterns on a semiconductor wafer at a time and cutting the semiconductor wafer into individual chips. An inspection apparatus to which the present invention is applied uses a laser beam to observe a semiconductor wafer under a microscope to detect various types of defects present in the semiconductor wafer, and to inspect a resist formed on the semiconductor wafer in a lithography step of a semiconductor process. It is to inspect or measure the fine dimensions, overlay accuracy, and the like of the pattern and the circuit pattern formed by etching using this resist pattern.

FIG. 1 shows a schematic configuration of an inspection apparatus to which the present invention is applied. The inspection apparatus 1 shown in FIG. 1 includes a movable stage 2 that movably supports a semiconductor wafer 100 at an arbitrary position.

The movable stage 2 includes, for example, an X, Y stage for moving the semiconductor wafer 100 mounted on the movable stage 2 in the horizontal direction, and a Z stage for moving the semiconductor wafer 100 in the vertical direction. And a θ stage for rotating the semiconductor wafer 100, and a suction plate for sucking and fixing the semiconductor wafer 100. In the movable stage 2, each of the stages is operated under the control of the control unit 3. By driving each of the stages, an arbitrary part of the semiconductor wafer 100 sucked by the suction plate is moved. The inspection position is moved to a predetermined inspection position of the inspection apparatus 1 and the height direction of the semiconductor wafer 100 is appropriately adjusted, so that the focus state can be adjusted to an optimum state.

Further, the inspection apparatus 1 includes an illumination light source 4 for emitting illumination light for illuminating an arbitrary inspection location on the semiconductor wafer 100 positioned at a predetermined inspection location.

As the illumination light source 4, for example, an ultraviolet solid laser is used. This ultraviolet solid-state laser converts the wavelength of laser light emitted from a solid-state laser such as a YAG laser using a non-linear optical element, for example, a deep ultraviolet (DUV) having a wavelength of about 266 nm or 193 nm.
Ultra Violet) laser light is emitted.

The resolution of the optical microscope depends on the wavelength of the illumination light irradiated on the inspection object and the NA of the objective lens. The wavelength of the illumination light is short, and the higher the NA of the objective lens, the higher the optical resolution. improves. In the inspection apparatus 1 to which the present invention is applied, an ultraviolet solid-state laser is used as the illumination light source 4 to illuminate an inspection location on the semiconductor wafer 100 with a short-wavelength DUV laser beam, and a high NA objective lens is used. Is used, a high resolution can be obtained, and a fine pattern can be inspected with high accuracy. Further, the ultraviolet solid-state laser has a small apparatus itself, and further has, for example, wavelength stability, monochromaticity, compared with an excimer laser used in a lithography process.
It is also excellent in beam profile, cooling measures, gas replenishment measures, laser safety measures, handling convenience, and the like, and is optimal as the illumination light source 4 in the inspection apparatus 1.

The inspection apparatus 1 includes an illumination optical system for irradiating a DUV laser beam emitted from the illumination light source 4 to an inspection location on the semiconductor wafer 100 to illuminate the inspection location, and a DUV laser beam. An imaging optical system that guides reflected light, scattered light, diffracted light, and the like from the illuminated inspection location to the imaging element 5 and forms an image of the inspection location on the imaging element 5 is provided.

Here, each optical element constituting the illumination optical system and the imaging optical system will be described. The DUV laser light emitted from the illumination light source 4 first passes through a variable ND filter (darkening filter) 6 and enters a condenser lens 7. Here, the variable ND filter 6 attenuates the DUV laser light emitted from the illumination light source 4 without changing the spectral composition.

The DUV laser light incident on the condenser lens 7 is condensed by the condenser lens 7 and forms an image inside the shutter 8. The shutter 8 includes, for example, an acousto-optic modulator (AOM), and switches the transmission or blocking of the DUV laser light under the control of the control unit 3. The acousto-optic modulator is an optical modulator utilizing an acousto-optic effect, and is capable of freely modulating diffracted light within a range of diffraction efficiency.
If the 0th-order diffracted light from the acousto-optic modulator is blocked and only the 1st-order diffracted light is extracted using a spatial filter, a shutter with extremely high responsiveness can be configured. By switching the transmission or blocking of the DUV laser light by the shutter 8, the light amount of the DUV laser light transmitted through the shutter 8 is adjusted, and the irradiation light amount of the DUV laser light irradiated on the inspection location on the semiconductor wafer 100 is adjusted. Will be.

When a fine dimension measurement of a resist pattern formed on a semiconductor wafer 100 in a lithography step of a semiconductor process is performed using the inspection apparatus 1,
Since the resist pattern to be inspected is irradiated with DUV laser light close to the exposure wavelength, it is important to control the amount of DUV laser light irradiation in order to prevent the resist pattern from shrinking. is there. Therefore, in the inspection apparatus 1, a shutter 8 is provided in the optical path of the DUV laser light, and the shutter 8 switches transmission or cutoff of the DUV laser light under the control of the control unit 3, thereby irradiating the DUV laser light. The amount of light is adjusted.

The shutter 8 may be any shutter as long as it can switch between transmitting and blocking the DUV laser light emitted from the illumination light source 4.
For example, a spatial light modulator such as a liquid crystal panel using a liquid crystal material, a light diffraction type shutter using a diffraction grating, a waveguide type shutter using a photoelastic effect, or the like may be used.

The DUV laser light transmitted through the shutter 8 is
The light is applied to the diffusion surface of the rotary diffusion plate 10 via the optical fiber 9. Here, the optical fiber 8 guides the DUV laser light emitted from the illumination light source 4 to each subsequent optical element in a flexible manner, and randomly changes the polarization direction of the DUV laser light emitted from the illumination light source 4 in a linearly polarized state. This is for converting the DUV laser light incident in the single mode into the multi mode. Also, the rotating diffusion plate 10
Is to reduce speckle noise, which is a problem when using DUV laser light having good coherence as illumination light. In any case, the coherence of the illumination optical system is reduced, and functions as coherence reduction means for obtaining uniform illumination.

The DUV laser light applied to the rotary diffusion plate 10 sequentially passes through a condenser lens 11, an aperture stop 12, a field stop 13, and a condenser lens 14 constituting a Koehler illumination system using the rotary diffusion plate 10 as a light source. And enters the polarization beam splitter 15.

DU incident on the polarizing beam splitter 15
The V laser light is split into two linearly polarized light components orthogonal to each other by the polarization beam splitter 15, one of which is reflected by the polarization beam splitter 15, and the other passes through the polarization beam splitter 15.

One linearly polarized light component reflected by the polarization beam splitter 15 is converted into circularly polarized light by passing through a quarter-wave plate 16, and is converted into a predetermined light on a semiconductor wafer 100 via an objective lens 17. Irradiated at inspection locations. As a result, a predetermined inspection location on the semiconductor wafer 100 is illuminated by the DUV laser light. In this inspection device 1, an illumination optical system is configured by each optical element from the variable ND filter 6 to the objective lens 17 described above.

The other linearly polarized light component transmitted through the polarization beam splitter 15 is incident on a light quantity monitor 19 via an imaging lens 18 and received by the light quantity monitor 19. Here, the other linearly polarized light component transmitted through the polarization beam splitter 15 and received by the light amount monitor 19 is reflected by the polarization beam splitter 15 under the condition that the polarization dependency of the illumination light source 4 is constant. A proportional relationship is established with the light of one linearly polarized light component irradiated on the inspection location on the wafer 100. Therefore, if the correlation between these lights is obtained in advance, the light amount monitor 1
9, the DU irradiating the inspection location on the semiconductor wafer 100 from the amount of light of the other linearly polarized light component received by
The irradiation light amount of the V laser beam can be obtained.

As the light amount monitor 19 for monitoring the irradiation light amount of the DUV laser light, for example, a CCD (charge-coupled device) camera for ultraviolet light configured to obtain high sensitivity to deep ultraviolet laser light is used. Used. The light amount monitor 19 is connected to the integrating circuit 20 and converts the received light into an electric signal.
To be supplied. The integrating circuit 20 calculates the integrated irradiation light amount of the DUV laser light from the electric signal supplied from the light amount monitor 19 and supplies the calculated irradiation light amount to the control unit 3.

As the light amount monitor 19, any monitor can be used as long as it can convert the received light into an electric signal. For example, a phototransistor, a calorimeter, or the like may be used as the light amount monitor 19.

In the inspection apparatus 1, the control unit 3 controls the shutter 8 in accordance with the integrated irradiation light amount of the DUV laser light calculated by the integration circuit 20, and irradiates the inspection spot on the semiconductor wafer 100 with the DUV. The irradiation light amount of the laser beam is adjusted. For example, as described above, the semiconductor wafer 1
When measuring the fine dimensions of the resist pattern formed on the resist pattern 00, when the integrated irradiation light amount of the DUV laser light calculated by the integration circuit 20 approaches the irradiation threshold value that causes the resist pattern to shrink, the control unit 3 Then, the shutter 8 is closed to block the DUV laser light so that the DUV laser light is not irradiated on the resist pattern. Further, the control unit 3 can also adjust the irradiation light amount of the DUV laser light irradiated on the resist pattern by controlling the variable ND filter 6.

In the inspection apparatus 1, the control unit 3
It is also possible to control the opening / closing operation of the shutter 8 in the illumination optical system in synchronization with the shutter of the image pickup device 5 composed of an ultraviolet CCD camera or the like. As described above, if the opening and closing operation of the shutter 8 in the illumination optical system is controlled in synchronization with the shutter of the image pickup device 5, the semiconductor wafer 1
The DUV laser light can be efficiently radiated to the inspection location on the 00.

In the inspection apparatus 1, the illumination light source 3
From the illumination optical system, the imaging lens 18 and the light amount monitor 1
9, each unit including the integrating circuit 20 and the control unit 3 functions as lighting means.

The DUV laser light applied to a predetermined inspection location on the semiconductor wafer 100 is reflected, scattered, and diffracted according to the state of the inspection location. The reflected light, scattered light, and diffracted light from these inspection points pass through the objective lens 17 and enter the quarter-wave plate 16. Then, after being converted into linearly polarized light by the 波長 wavelength plate 16, the light enters the polarization beam splitter 15 again. Here, reflected light from the inspection location that has re-entered the polarization beam splitter 15,
Since the scattered light and the diffracted light are linearly polarized light components orthogonal to the linearly polarized light components reflected by the polarization beam splitter 15, they pass through the polarization beam splitter 15.

The reflected light, the scattered light and the diffracted light from the inspection site transmitted through the polarizing beam splitter 15 are transmitted to the imaging lens 21.
And enters the image pickup device 5 via the. Thereby, the image of the inspection location enlarged by the objective lens 17 is captured by the image capturing element 5.

In this inspection apparatus 1, the objective lens 1
Each optical element from 7 to the imaging lens 21 forms an imaging optical system. The imaging optical system and the image pickup device 5 function as detection means.

Here, as the objective lens 17, for example, a lens having a high numerical aperture NA of about 0.9 is used. In this inspection apparatus 1, a short-wavelength DUV laser beam is used as illumination light, and a high-numerical-aperture lens is used as the objective lens 17, so that a fine pattern can be inspected with high accuracy. The objective lens 17 is provided with a countermeasure to reduce aberrations with respect to, for example, DUV laser light having a wavelength of 266 nm.

As the image pickup device 5, for example,
A high-sensitivity ultraviolet light CCD camera capable of obtaining a quantum efficiency of about 36% with respect to DUV laser light is used. As described above, if a CCD camera having high sensitivity to DUV laser light is used as the image pickup device 5, a fine pattern image can be taken at high resolution. This image pickup device 5 is connected to an image processing computer 22. In the inspection apparatus 1, the image of the inspection location on the semiconductor wafer 100 taken by the image pickup device 5 is taken into the image processing computer 22.

It is desirable that the image pickup device 5 has a cooling mechanism. For example, C for ultraviolet light
When a CD camera is used as the image pickup device 5, C
It is desirable that the CD chip be cooled to about 5 ° C. by a Peltier element. If the image pickup device 5 is cooled as described above, read noise or the like generated when the image of the inspection location on the semiconductor wafer 100 picked up by the image pickup device 5 is transferred to the image processing computer 22 can be reduced. Thermal noise can be greatly reduced.

In the inspection apparatus 1, as described above, an image is formed on the image pickup device 5 by the image forming optical system, and the semiconductor wafer 100 picked up by the image pickup device 5 is picked up.
The image of the inspection point above is supplied to the image processing computer 22. Then, the image of the inspection location is subjected to image processing by the image processing computer 22 and analyzed, whereby the state of the inspection location is inspected. That is, in this inspection apparatus 1, the image processing computer 2
Reference numeral 2 functions as an inspection unit, and the state of an inspection location on the semiconductor wafer 100 is inspected by the image processing computer 22.

Specifically, for example, the semiconductor wafer 100
In the case of detecting a defect existing in an image, an image of a defective portion (defect image) and an image of a non-defect portion having the same pattern (reference image) are respectively captured. By calculating the difference between the defect image and the reference image, the difference is detected as a defect existing in the semiconductor wafer 100. Also,
When inspecting or measuring a resist pattern formed on the semiconductor wafer 100 in a lithography process of a semiconductor process, or a fine dimension, overlay accuracy, or the like of a circuit pattern formed by etching using the resist pattern, an image is required. The image of the inspection location is image-processed by the processing computer 22, and a light intensity profile is created. Then, based on the light intensity profile, measurement of pattern dimensions, inspection of overlay accuracy, and the like are performed.

In the inspection apparatus 1, the illumination optical system is configured so that the focal length of the condenser lens 14 is sufficiently longer than the focal length of the objective lens 17. Therefore, the condenser lens 1
By removing 4, a critical illumination system is established by the rotating diffuser 10, the condenser lens 11, the aperture stop 12, and the objective lens 20, and a spatial image in the plane of the aperture stop 12 is formed on the semiconductor wafer 100. . That is, in the inspection apparatus 1, by switching the condenser lens 14 in and out, the illumination by the Koehler illumination system and the illumination by the critical illumination system can be switched. Note that when illuminating with the critical illumination system, the imaging position is different from that when illuminating with the Koehler illumination system, so that the movable stage 2 focuses on illumination with the Koehler illumination system and illumination with the critical illumination system. A stage stroke that can adjust the position difference is required. This inspection device 1
In, the illumination optical system from the rotating diffusion plate 10 to the objective lens 17 and the imaging optical system from the objective lens 17 to the imaging lens 21 constitute an infinite optical system, and are compared with the focal length of the objective lens 17. Since the focal length of the condenser lens 14 is sufficiently long, the difference between the focal positions is very small.

To switch the condenser lens 14 in and out, for example, the condenser lens 14 is attached to a revolver, and the revolver is rotated to move the condenser lens 14 on and off the optical path of the DUV laser light. It is performed by moving over the position. In this case, the revolver provided with the condenser lens 14 functions as an illumination system switching unit. The switching of the condenser lens 14 in and out is not limited to the above-described revolver type, but may be any method such as a slide type or a cam type as long as the condenser lens 14 can be freely inserted and removed. I do not care. Further, instead of removing the condenser lens 14, a Koehler illumination system may be switched to a critical illumination system by inserting a considerable lens. However, in this case, cosine 4
Since there is a problem that the peripheral light amount is reduced by the power law, a method of switching the Koehler illumination system to the critical illumination system is most appropriate to remove the condenser lens 14.

Generally, the illumination of the optical microscope is generally adjusted so as to provide uniform illumination on the surface to be inspected. In the inspection apparatus 1 as well, when actually inspecting an inspection location on the semiconductor wafer 100, the illumination optical system is used as a Koehler illumination system, and the inspection location on the semiconductor wafer 100 is uniformly irradiated with DUV laser light. Is desirable. On the other hand, the resolution of the optical system depends on the NA of the objective lens,
It is known that, in addition to the wavelength of the illumination light, the intensity largely depends on the intensity distribution of the illumination light in the illumination system aperture stop plane. Thus, in the inspection apparatus 1, the intensity distribution of the DUV laser light in the plane of the aperture stop 12 is set to be an optimum distribution according to the pattern shape of the inspection location on the semiconductor wafer 100 and the inspection purpose.

Here, the DUV in the plane of the aperture stop 12 is shown.
In order to optimize the intensity distribution of the laser beam, it is necessary to adjust the optical system. However, it is difficult to adjust such an optical system in the Koehler illumination system. That is, if the adjustment of the optical system is performed while observing the irradiation state of the DUV laser light, the adjustment of the optical system can be easily performed. However, in the Koehler illumination system, the image of the condenser lens 14 is inspected ( Therefore, an image is formed on the portion irradiated with the DUV laser light, and the optical system cannot be adjusted while observing the irradiation state of the DUV laser light. Therefore, in this case, it is necessary to adjust the optical system using a special adjustment jig different from the inspection device 1.

On the other hand, in the critical illumination system, an image in the plane of the aperture stop 12 is formed at an inspection position (a position irradiated with the DUV laser light). The adjustment of the optical system can be performed while doing so. Therefore, if the adjustment of the optical system is performed by the critical illumination system, for example, even during the inspection of the inspection location on the semiconductor wafer 100, a special setup change or the inspection apparatus 1 and The optical system can be appropriately and easily adjusted without using another adjustment jig. Therefore, in the inspection apparatus 1, when adjusting the optical system, the condenser lens 14 is removed to make the illumination optical system a critical illumination system so that the adjustment of the optical system can be performed appropriately and easily.

In the inspection apparatus 1, the aperture stop 1
Reference numeral 2 denotes a spatial filter stop (hereinafter referred to as a stop) having an arbitrary σ value (diameter of the aperture stop / pupil diameter of the objective lens) and a center with respect to the optical axis of the illumination optical system as shown in FIG. And a spatial filter stop (hereinafter referred to as a donut stop) having a shape obtained by combining annular zones having an arbitrary σ value. You can choose what you want.

Specifically, for example, the semiconductor wafer 100
In order to detect a defect existing in the pattern, an σ stop that exhibits an average frequency response with respect to the spatial frequency of the pattern at the inspection location is selected, and an illumination system using the σ stop (hereinafter referred to as σ illumination). The inspection location is illuminated by In the case of performing fine dimension measurement of a resist pattern formed on the semiconductor wafer 100 in a lithography process of a semiconductor process or a circuit pattern formed by etching using the resist pattern, the pattern of an inspection location is specified. A donut stop which shows a frequency response particularly sensitive to a spatial frequency is selected, and an inspection target is illuminated by an illumination system using the donut stop (hereinafter, referred to as a donut illumination), or a specific space of a pattern of an inspection location is selected. An σ stop that shows a frequency response particularly sensitive to frequency is selected, and the inspection target is illuminated by σ illumination using the σ stop.

Switching of the spatial filter aperture is performed, for example, by
Attach each spatial filter aperture such as the σ aperture and the donut aperture described above to the revolver, rotate this revolver,
This is performed by disposing the selected spatial filter stop on the optical path of the DUV laser light. In this case, the revolver to which each spatial filter stop is attached functions as a switching unit that switches the intensity distribution of the DUV laser light in the plane of the aperture stop 12. The switching of the spatial filter aperture is not limited to the revolver type as described above, and may be any type such as a slide type or a cam type as long as the spatial aperture filter can be switched arbitrarily. .

Further, the σ value of the σ stop and the σ value of the donut stop described above are determined according to the shape of the inspection portion of the inspection object to be inspected by the inspection apparatus 1 and the inspection purpose.
It is arbitrarily determined between 0.01 and 1.0. Also,
The number of σ-stops and donut stops to be incorporated into the inspection apparatus 1 as the aperture stop 12 is also arbitrarily determined according to the shape of the inspection location of the inspection object to be inspected by the inspection apparatus 1 and the inspection purpose. You.

In the inspection apparatus 1, as described above, the spatial filter aperture of the aperture stop 12 is switched in accordance with the pattern of the inspection location and the inspection purpose, and the intensity distribution of the DUV laser light in the plane of the aperture stop 12 is changed. Therefore, the state of the inspection location can be inspected with high resolution and with extremely high precision. Actually, a specific resist pattern formed on the semiconductor wafer 100 is illuminated by donut illumination using a donut stop as shown in FIG. 2, and the resist pattern is illuminated based on the intensity profile of light obtained from the image. As a result of performing fine dimension measurement, it was confirmed that the measurement could be performed with extremely high accuracy.

The inspection apparatus 1 further includes a focus control means for adjusting the distance between the objective lens 17 and the semiconductor wafer 100 to be inspected, that is, the focus state of the imaging optical system.

In an inspection apparatus using an ordinary optical microscope,
By irradiating the object with the illumination light and detecting the reflected light, the distance between the objective lens and the object is measured to adjust the focus state. If the focus state is adjusted while irradiating the object, the illuminating light at this time will also be integrated as the irradiation light amount on the inspection object. As described above, if the irradiation light amounts of the illumination light are integrated in the adjustment of the focus state, the illumination light amount at the time of performing an actual inspection is limited, which is very inefficient.

Therefore, in the inspection apparatus 1, the capacitance type sensor 23 is disposed near the objective lens 17, and the objective lens 17 and the semiconductor wafer 100 to be inspected are arranged by the capacitance type sensor 23. Of the movable stage 2 so that the distance between the objective lens 17 and the semiconductor wafer 100 is optimized based on the distance.
Is driven to adjust the focus state of the imaging optical system. That is, in the inspection device 1, the capacitance sensor 23, the control unit 3, and the Z stage of the movable stage 2 function as focus control means for adjusting the focus state of the imaging optical system.

Here, the semiconductor wafer 10 to be inspected is
0 is inclined in the height direction, or the semiconductor wafer 10
If the posture of the movable stage 2 supporting the object lens 17 is not maintained with high accuracy, the capacitance measuring the distance between the objective lens 17 and the semiconductor wafer 100 outside the optical axis of the objective lens 17 is measured. If there is only one type sensor 23, an Abbe error occurs and the objective lens 17 and the semiconductor wafer 100
Distance cannot be measured accurately. In particular, the short wavelength D
In the inspection apparatus 1 using UV laser light as illumination light and a lens with a high numerical aperture as the objective lens 17, the depth of focus of the optical system is very narrow, and even a slight displacement greatly affects inspection accuracy.

In particular, when the inspection apparatus 1 measures a fine dimension of a resist pattern formed on the semiconductor wafer 100 in a lithography step of a semiconductor process or a circuit pattern formed by etching using the resist pattern. However, even if the focus shift is within the depth of focus of the optical system, the focus error has a great effect on the measurement result. For this reason, there is a limit to performing fine dimension measurement with high accuracy only by performing the focus control as described above. Therefore, in the inspection apparatus 1, at the time of fine dimension measurement, the semiconductor wafer 100 is sequentially scanned in the vertical direction to perform fine dimension measurement, and the point at which the contrast of the fine pattern at the inspection location is maximized is determined by function fitting. To the accuracy of about 1/10 of the step width when sequentially scanning in the vertical direction,
Fine dimensions are measured.

Here, the focus accuracy is determined by the number of successive operation steps and the step width at this time, but when measuring the fine dimensions of the resist pattern formed on the semiconductor wafer 100, the focus wavelength is close to the exposure wavelength. It is necessary to reduce the irradiation light amount of the DUV laser light as much as possible. For this reason, it is desired that the number of successive scanning steps be minimized so as to satisfy the function fitting accuracy of the contrast. Furthermore, in order to increase the function fitting accuracy for finding the maximum contrast point of the fine pattern at the inspection location, it is desirable that the step width be small. Due to such restrictions, the inspection apparatus 1 needs a focus accuracy of about 50 nm.

For this reason, in the inspection apparatus 1, as shown in FIG. 3, a plurality of capacitance type sensors 23 are arranged at target positions with respect to the optical axis of the objective lens 17 to reduce Abbe error. Like that. Note that the capacitance type sensor 23
The number of is not limited to two as shown in FIG. 3, and any number may be arranged as long as the position of the center of gravity of the capacitance type sensor 23 coincides with the center of the optical axis of the objective lens 17. . Further, as shown in FIG. 4, a plurality of capacitance type sensors 23 arranged symmetrically with respect to the optical axis of the objective lens 17 may be combined. In this case, when measuring the outer periphery of the semiconductor wafer 100, the capacitance type sensor 23
Even in a region where the semiconductor device 100 protrudes from the semiconductor wafer 100, the outputs of the plurality of capacitance type sensors 23 complement each other, so that measurement over the entire surface of the semiconductor wafer 100 is possible.

The capacitance type sensor 23 converts the capacitance between the measurement probe and the semiconductor wafer 100 to be inspected into a voltage value and outputs the voltage value. The output voltage is proportional to the distance between the measurement probe and the semiconductor wafer 100. Further, the capacitance between the measurement probe and the semiconductor wafer 100 also changes depending on the dielectric constant of the medium between the measurement probe and the semiconductor wafer 100.

In this inspection apparatus 1, the capacitance type sensor 2
It is known that the measurement probe of No. 3 and the semiconductor wafer 100 are both in the air atmosphere, and the dielectric constant of the air changes depending on environmental parameters such as temperature and humidity. Further, it also changes due to the thermal expansion of the cable between the measurement probe of the capacitance type sensor 23 and the amplifier. For this reason, in the inspection device 1, among these environmental parameters,
The focus accuracy is improved by monitoring temperature, humidity, and the like, and feeding back to the output value of the capacitance type sensor 23.

The Abbe error and the semiconductor wafer 1
The reduction of the error due to the tilt of 00 and the compensation of the temperature and humidity dependencies of the capacitance type sensor 23 can be appropriately performed by the above-described method, but in the state where the movable stage 2 is held on the suction plate. In the case where the flatness of the surface of the semiconductor wafer 100 is poor and there is a surface waviness higher than the focus accuracy within the installation interval of the capacitance type sensor 23, the inspection device 1 does not monitor the flatness information. Unless some kind of error feedback is performed, the focus accuracy will deteriorate. Here, the flatness of the semiconductor wafer 100 is separately defined by a standard, and what affects the focus accuracy is mainly the flatness of the suction plate in a state where the suction plate is mounted on the movable stage 2.

Therefore, in the inspection apparatus 1, the flatness of the suction plate is interpolated in order to secure the required focus accuracy. Specifically, the inspection device 1
Then, the above-mentioned illumination optical system is changed to a critical illumination system by removing the condenser lens 14, and a processing algorithm at the time of measuring the fine dimensions is applied by using a light source image formed on the semiconductor wafer 100 by the critical illumination system. Then, the flatness interpolation data of the suction plate is obtained.

The light source image formed on the semiconductor wafer 100 contains a large number of speckle noises of the DUV laser light on the rotary diffusion plate 10 as shown in FIG. 5, for example. Note that FIG. 5 shows light development in which an image is formed on the semiconductor wafer 100 by the above-described donut illumination.
Here, when the sequential operation in the vertical direction of the movable stage 2 included in the processing algorithm at the time of measuring the fine dimensions is performed,
With the change in the focus state, as shown in FIG. 6, for example, parameters such as the intensity dispersion of each pixel of the image pickup device 5 have an extreme value at a certain point. FIG. 6 shows the variance of the pixel intensity obtained when observing the portion A in FIG. 5 while performing the sequential operation of the movable stage 2 in the vertical direction, and the vertical axis represents the pixel intensity. The variance value and the horizontal axis indicate the position of the movable stage 2 in the vertical direction.

By applying fitting to the parameter measured as described above, the extreme value of the parameter can be obtained with a substep width. If the distance between the movable stage 2 and the objective lens 17 at this time, that is, the difference between the output of the capacitance type sensor 23 and the output of the capacitance type sensor 23 at the focus target value is obtained, the value is obtained at the observation position. The flatness interpolation data of the suction plate can be used. This operation is performed at appropriate step intervals within the surface of the semiconductor wafer 100, and based on the obtained flat life data of the suction plate at each observation position, for example, spline interpolation or the like is performed, so that the semiconductor wafer 100 The flatness interpolation data of the suction plate at an arbitrary measurement point can be used.

The semiconductor wafer 100 is preferably a bare wafer having a uniform reflectivity and good flatness. The flat wafer having a uniform reflectivity is not limited to a bare wafer, and may be a plane mirror or the like. The above measurement is performed on the semiconductor wafer 100
Is rotated and measured a plurality of times to obtain the semiconductor wafer 10.
An error component caused by 0 can be removed. For example, the semiconductor wafer 100 is rotated 90 degrees, and the flatness interpolation data of the suction plate is acquired. 180 degrees,
The flatness interpolation data of the suction plate is obtained even at the rotation position of 270 degrees, and the flatness interpolation data of the suction plate obtained at the rotation positions of 0, 90, 180, and 270 degrees is converted into a rotation component, Extract non-rotated components for each component. Of these, the rotation component is an error component due to the semiconductor wafer 100, and the non-rotation component from which the rotation component has been removed is used as the final flatness interpolation data of the suction plate in the inspection apparatus 1.

When acquiring the flatness interpolation data of the suction plate as described above, the illumination optical system is switched to the critical illumination system and the light source image is formed on the semiconductor wafer 100 as described above. By observing the image. Semiconductor wafer 100 on which a predetermined pattern is formed
When observing is performed, if the suction plate flatness interpolation data is acquired by the above-described method, a pattern must be drawn at the position where the data is acquired. This imposes restrictions on the acquisition of the suction plate flatness interpolation data. Furthermore, when the flatness interpolation data of the suction plate is acquired by the Koehler illumination system in the same manner, the DUV laser light is illuminated parallel to the semiconductor wafer 100 even in the defocused state in the Koehler illumination system. Therefore, there is little difference in light amount, and the defocus characteristic varies depending on the spatial frequency of the pattern, and it is difficult to find an extreme value. For this reason, it is difficult to accurately acquire the flatness interpolation data of the suction plate.

For the reasons described above, when acquiring the flatness interpolation data of the suction plate, the illumination optical system is switched to the critical illumination system, a light source image is formed on the semiconductor wafer 100, and the image is formed. It is desirable to perform this by observing.

In the above description, the example in which the capacitance type sensor 23 is used as the distance sensor for detecting the distance between the objective lens 17 and the semiconductor wafer 100 to be inspected has been described. Any device that can measure the distance between the objective lens 17 and the semiconductor wafer 100 with high accuracy may be used. For example, a working transformer type displacement meter, an eddy current type displacement meter, a displacement meter using an atomic force probe, a pneumatic displacement meter, or the like may be used as the distance sensor.

As described above, in the inspection apparatus 1 to which the present invention is applied, the intensity distribution of the DUV laser light in the surface of the aperture stop 12 is arbitrarily manipulated to optimize the distribution of the DUV laser light in accordance with the pattern of the inspection location and the inspection purpose. By making it distribution,
The state of the inspection location can be inspected with high resolution and extremely high accuracy. For example, it becomes possible to accurately measure very fine pattern dimensions and the like that could not be measured conventionally. That is, the K-factor for determining the imaging limit (imaging limit = K × λ) is obtained by setting the intensity distribution of the DUV laser light in the plane of the aperture stop 12 to an optimum distribution according to the pattern of the inspection location and the inspection purpose. / NA) can be reduced. Decreasing the K factor is equivalent to shortening the illumination wavelength λ or increasing the numerical aperture NA of the objective lens, and compared to shortening the illumination wavelength λ and increasing the NA of the objective lens. Can be realized at a much lower cost.

Further, in this inspection apparatus 1, by switching the illumination optical system to the critical illumination system and adjusting the optical system, for example, even during the inspection, it is possible to use an appropriate adjustment jig without using a special adjustment jig. Further, it is possible to easily adjust the optical system. Therefore, the maintenance work time of the optical system, such as the work of replacing the illumination light source 3 and the optical fiber 9, which has conventionally required advanced adjustment technology and time, can be greatly reduced.

Further, in the inspection apparatus 1, focus control can be performed with much higher precision than the depth of focus of the optical system. In particular, the dimension measurement of a fine pattern can be performed with extremely high precision.

[0081]

According to the inspection apparatus of the present invention, the intensity distribution of the illumination light in the aperture stop plane of the illumination means is switched to the optimum distribution according to the structure of the inspection location of the inspection object and the inspection purpose. Therefore, the state of the inspection location can be inspected with high resolution and with extremely high accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of an inspection apparatus to which the present invention is applied.

FIG. 2 is a plan view showing an example of a donut stop provided in the illumination optical system of the inspection device.

FIG. 3 is a plan view showing an example of an arrangement of capacitance sensors provided in the inspection device.

FIG. 4 is a plan view showing another example of the arrangement of the capacitance type sensors provided in the inspection device.

FIG. 5 is a diagram showing light development formed on a semiconductor wafer by donut illumination using the donut stop.

FIG. 6 is a diagram showing a variance of pixel intensities of the image pickup device obtained when observing a portion A in FIG. 5 while sequentially performing a vertical operation of a movable stage provided in the inspection apparatus.

[Explanation of symbols]

1 inspection device, 2 movable stage, 3 control unit,
4 illumination light source, 5 image pickup device, 6 variable ND filter, 7 condenser lens, 8 shutter,
Reference Signs List 9 optical fiber, 10 rotating diffuser, 11 condenser lens, 12 aperture stop, 13 field stop, 1
4 condenser lens, 15 polarizing beam splitter, 16 quarter-wave plate, 17 objective lens, 1
Reference Signs List 8 imaging lens, 19 light quantity monitor, 20 integrating circuit, 21 imaging lens, 22 image processing computer, 23 capacitance type sensor

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) H01L 21/66 H01L 21/30 502V F term (reference) 2F065 AA21 AA56 BB02 BB03 CC19 FF04 FF42 FF48 FF49 FF67 GG04 GG17 GG22 HH09 HH13 JJ01 JJ03 JJ05 JJ09 JJ15 JJ26 LL02 LL04 LL24 LL30 LL36 LL37 LL49 LL57 NN01 NN08 NN16 PP12 PP13 QQ25 QQ31 RR01 RR02 UU01 2H052 AC02 AC03 AC12 AC14 AC15 AC25 AC26 DB14 AC14 DB12 AC14 DJ04 DJ06 DJ07

Claims (8)

[Claims] 1. A supporting means for supporting an object to be inspected, an illuminating means for irradiating monochromatic light in a predetermined wavelength range as illumination light to an inspection location of the object supported by the supporting means, and the illuminating light Detecting means for detecting reflected light, scattered light, and diffracted light from the inspection location illuminated by the inspection means; and inspection means for inspecting the state of the inspection location based on an output from the detection means, An inspection apparatus characterized by comprising switching means for switching the intensity distribution of the illumination light in the plane of the aperture stop according to the structure of the inspection location and the purpose of the inspection. 2. An inspection apparatus according to claim 1, wherein said illuminating means has an ultraviolet laser light source for emitting laser light in an ultraviolet wavelength range. 3. An illumination system switching means for switching between a first illumination system for illuminating the inspection location with Koehler illumination and a second illumination system for illuminating the inspection location with critical illumination. The inspection device according to claim 1, further comprising: 4. The inspection apparatus according to claim 1, wherein said illuminating means has a coherence reducing means for reducing the coherence of said illumination light. 5. The lighting device according to claim 4, wherein the illuminating means has a rotating diffuser as the coherence reducing means.
Inspection device as described. 6. The inspection apparatus according to claim 4, wherein the illuminating means has an optical fiber for converting incident light from a single mode to a multi-mode and outputting the converted light, as the coherence reducing means. . 7. The illumination unit includes a light amount monitoring unit that monitors a light amount of the illumination light, and a shutter unit that switches transmission or blocking of the illumination light according to the light amount of the illumination light detected by the light amount monitoring unit. The inspection device according to claim 1, further comprising: 8. A focus control unit for controlling a focus state between the detection unit and an inspection position of the inspection object supported by the support unit based on an output from a distance sensor, wherein the focus control unit includes: By switching the illuminating means to the second illuminating system, based on information obtained by illuminating the inspection location with critical illumination, a focus error amount caused by the accuracy of the supporting surface of the supporting means is detected. The inspection apparatus according to claim 3, wherein the focus control is performed by correcting an output from the distance sensor according to the error amount.